CF4, C2F6, NF3 and SF6 are commonly used in the semiconductor and flat panel display manufacturing industries, for example, in dielectric layer etching and chamber cleaning. Following the manufacturing or cleaning process there is typically a residual PFC content in the effluent gas stream pumped from the process tool. PFCs are difficult to remove from the effluent stream, and their release into the environment is undesirable because they are known to have relatively high greenhouse activity.
As illustrated in FIG. 1, it is known to provide an abatement device for treating such gases exhaust from process tools. In the illustrated example, the abatement device 200 is located downstream from one or more evacuation systems each for evacuating a respective process chamber 202 of a process tool. In this example, each evacuation system comprises a Roots blower 204 or other secondary pump for drawing the effluent stream from the process chamber 202, the Roots blower 204 being backed by a multi-stage dry pump 206 that exhausts the effluent stream at or around atmospheric pressure to the abatement device 200. A suitable backing pump 206 comprises a combination of Roots and Northey (“claw”) type pumping mechanisms.
The object of the abatement is to convert relatively harmful components of the effluent stream into compounds that are less harmful to the environment and/or into compounds that can be more conveniently disposed of, for example, by a wet scrubber (not shown) located downstream from the abatement device 200. Conventional abatement devices include incineration, plasma abatement and thermal decomposition tools.
Semiconductor manufacturing processes typically produce as by-products particulates or powders that are drawn from the process chamber 202 by the to evacuation system. As the pumping mechanisms of the backing pump 206 require close tolerances to be maintained between the rotor and stator components of the pumping stages during use, it is normal practice to inject an inert purge gas, such as nitrogen, into the pumping mechanisms. This purge gas serves to reduce the level of by-product contamination of the backing pump 206. However, in view of the relatively high flow rates of purge gas into each backing pump 206 (typically around 40 to 50 slm) in comparison to the flow rate of the effluent stream exhaust from each process tool 202 (typically around 5 slm), the injection of purge gas into one or more of the backing pumps 206 significantly increases the power requirement of the abatement device 200, as abatement of an effluent stream containing 70 to 90% purge gas requires significantly more power than the abatement of an effluent stream containing no purge gas.
It is an aim of at least the preferred embodiment of the present invention to seek to provide a relatively simple, efficient and low cost technique for treating an effluent gas stream from a process tool.